A look at the explosives used in the New York bombing

Initial reports about a device used in Saturday’s bombing in New York City suggested the explosive could have been a commercially available material called Tannerite. Stories from the Associated Press and New York Times reported the claim, citing anonymous officials involved in the investigation of the attack that injured 31.

But, on the basis of the material’s properties, explosives experts and the makers of Tannerite doubt it alone could have caused the explosion. A subsequent report from the New York Times seemed to confirm these doubts, indicating that officials had detected the explosive hexamethylene triperoxide diamine (HMTD) in devices related to the attack.

The suspected bomber, Ahmad Khan Rahami, was arrested after a shootout in New Jersey on Monday. He allegedly set off bombs in New Jersey and in New York on Saturday. According to news reports, anonymous officials identified Tannerite at the New York bomb site, and a second report linked HMTD to both bombings.

Tannerite, made and sold by Tannerite Sports, is used to produce exploding targets for long-range shooting practice. The targets explode when hit by a bullet, allowing shooters to hear and see that they’ve successfully made the shot. Occasionally, “tannerite” is used to describe similar products.

An exploding Tannerite target consists of an 8:1 ratio of oxidizer to catalyst, which come in separate containers and are mixed and shaken together prior to use. The Tannerite patent says that, in the optimal composition, the oxidizer contains 85% ammonium nitrate powder by weight, and 15% ammonium perchlorate. The catalyst is 90% explosive grade aluminum powder, 5% titanium sponge, and 5% zirconium hydride.

Jimmie C. Oxley, an explosive specialist at the University of Rhode Island, says that using Tannerite wouldn’t require chemistry training. “It is one of the less hazardous explosives to work with,” she says. But she doubts it was the sole explosive used in New York.

“It is impossible,” says Daniel Tanner, CEO of Tannerite Sports. Only a high-velocity bullet travelling at a minimum of 610 meters per second can trigger their exploding targets to go off. Tannerite is also resistant to fire, friction, and hard impacts. It cannot be merely jolted into exploding, suggesting that normal bomb triggers wouldn’t set it off. Furthermore, Tanner says finding aluminum or ammonium nitrate residue isn’t enough to say Tannerite was used. “Tannerite is not a compound,” he says. “It is a trademark.”

“Tannerite is not going to go off by itself,” Oxley says. “It is very stable stuff. You are going to have to put a strong initiating shock into it. And that could be provided by HMTD.”

HMTD is an organic explosive similar to triacetone triperoxide, the explosive used in the 2015 Paris attacks and the 2016 Brussels bombings. “HMTD is not stable and not nice stuff. You can easily set it off,” Oxley says. “To use HMTD there has to be some synthesis involved,” she says. Thus far, there are no reports as to how Rahami could have made or obtained HMTD for use in the bombs.

Anyone can buy Tannerite online or at sporting goods stores and gun shops. It is not regulated by the Bureau of Alcohol, Tobacco, Firearms & Explosives because the oxidizer and catalyst parts alone are not considered explosives. One state, Maryland, bans the sale, use, and ownership of exploding targets without an explosives license.

Law enforcement officials in the past have considered exploding targets as potential sources of bomb-making materials. A 2013 FBI bulletin on exploding targets concluded that they could serve as an alternative source of ammonium nitrate, which was used to make the bombs involved in the 1996 Oklahoma City bombing.

UPDATE: This story was updated on Sep. 21, 2016, with new information about the number of people injured in the New York City bombing.